1. Field of the Invention
The present invention relates generally to motorized surgical handpieces including pressurized labyrinth seals and a hollow, motor driven rotatable output shaft with a through bore for receiving a shank of a surgical tool in driving engagement.
2. Brief Discussion of the Related Art
Motorized surgical handpieces are commonly used to rotatably drive surgical tools, such as drills and burs, to perform a cutting operation on anatomical tissue at a surgical site. Motorized surgical handpieces typically include a motor contained in the interior of a housing of the handpiece and an output shaft driven by the motor in rotation for being coupled to a shank of a surgical tool in driving engagement. The surgical tool typically includes the shank and a cutter carried by the shank to perform a cutting operation on anatomical tissue when the shank is rotatably driven by the output shaft. Depending on the cutting operation to be performed and the type of anatomical tissue to be cut with the cutter, it is oftentimes necessary for the output shaft to rotate the surgical tool at considerably high speeds. As a result of the cutting operation, debris including fluid and anatomical tissue is normally generated at the surgical site.
It is advantageous for the surgical tool to be removably or releasably coupled with the output shaft so that various different types of surgical tools can be selectively coupled with the output shaft interchangeably. In many motorized surgical handpieces, the output shaft is solid and the handpiece includes a separate coupling, such as a chuck, attached to the output shaft for releasably holding the shank of the tool in a cavity of the coupling to establish driving engagement between the output shaft and the surgical tool. The output shaft is not in direct driving engagement with the surgical tool but, rather, is indirectly engaged with the surgical tool via the intermediary of the separate coupling. Since the output shaft is solid, the cavity terminates at a blind end within the coupling.
Motorized surgical handpieces that have a solid output shaft and a separate coupling on the output shaft for receiving a shank of the surgical tool in a cavity of the coupling are particularly susceptible to problems arising from the entry of debris into the coupling. During the cutting operation, debris may travel along the shank of the surgical tool toward the coupling and may enter the cavity of the coupling around the shank of the surgical tool. The blind end of the cavity within the coupling undesirably promotes the accumulation of debris in the coupling. A conventional approach to cleaning the coupling of debris involves removing the shank of the surgical tool from the cavity, pushing a bore brush into the vacated cavity, and withdrawing the bore brush from the cavity in hope that most of the debris will have attached itself to the bristles of the brush and will be removed from the cavity as the brush is withdrawn. It is unavoidable, however, that during the cleaning process some of the debris will be pushed by the brush further into the cavity and will become trapped in the blind end of the cavity. As a result of repeated use and cleaning of the handpiece over time, debris trapped in the cavity of the coupling will build up to the point where the shank of the surgical tool cannot be properly maintained in the cavity of the coupling or be properly driven by the output shaft. Another approach to cleaning the cavity of debris involves disassembling the handpiece, which ordinarily must be performed at the manufacturer's facility at considerable inconvenience, time and expense.
An additional drawback to conventional motorized surgical handpieces relates to their inability to effectively seal the interior of the handpiece from foreign substances including contaminants, such as the debris generated by the cutting operation, and cleaning substances. Consequently, the life of the motor in many motorized surgical handpieces is often prematurely shortened due to the exposure to foreign substances such as contaminants and cleaning substances, especially given the need for the handpieces to be sterilized to medical standards after each use. In motorized surgical handpieces where seals are provided on the output shaft, the seals produce friction that undesirably limits the rotational speed of the output shaft and, therefore, the rotational speed of the surgical tool.
Surgical cutting instruments having hollow driven shafts have been proposed, as represented by U.S. Pat. No. 2,144,342 to Morrison, U.S. Pat. No. 3,049,018 to Lusskin et al, U.S. Pat. No. 3,120,845 to Horner, U.S. Pat. No. 4,736,742 to Alexson et al, and U.S. Pat. No. 5,207,697 to Carusillo et al. The Horner, Alexson et al and Carusillo et al patents disclose motorized handpieces, but the handpieces do not incorporate non-contacting seals to seal the motors and the interiors of the handpieces from foreign substances. U.S. Pat. No. 3,082,009 to Whitley et al, U.S. Pat. No. 3,302,951 to Olesen, U.S. Pat. No. 3,804,423 to Booy, U.S. Pat. No. 4,565,378 to Wehfritz et al, U.S. Pat. No. 4,913,447 to Jostlein, U.S. Pat. No. 5,540,447 to Schultz et al, and U.S. Pat. No. 5,794,942 to Vance et al are illustrative of rotating shafts associated with air pressurized or labyrinth seals. In the Whitley et al, Olesen, Booy, Jostlein, Schultz et al and Vance et al patents, the seals are not attached to and do not rotate with the shafts. In the Wehfritz patent, air pressure is used to separate normally contacting sealing surfaces.
In view of the above, there is a need for a motorized surgical handpiece wherein the motor driven output shaft has a through bore defining a portion of a continuous lumen extending entirely through the handpiece to allow for insertion of a bore brush through the lumen for cleaning. The need also exists for a motorized surgical handpiece which has, in addition to the aforementioned continuous lumen, a pair of labyrinth seals including rotor seal components respectively attached to the rotatable output shaft at forward and rearward ends of the motor and stator seal components separated from the rotor seal components by a labyrinthine clearance to which pressurized air can be supplied to force foreign substances away from the motor during use and during cleaning after use.